Routing feedback loop example?

[Vadym Belyayev]

Hello everyone.

I came across this when setting a simple lab for CCNP and wanted to ask if in the example below you see a real issue.

This is about the route feedback loop.

1. A and B both redistribute RIPv2 into OSPF and OSPF into RIPv2 domain.

2. Route feedback issue should occur if we do not use a route-map here preventing the E2 192.168.1.0 to be redistributed back to RIPv2 domain.

However, I cannot understand what kind of an issue we have here.

All the pure RIPv2 routers keep the same path toward 192.168.1.0. Nothing strange here, like them going through A or B to reach 192.168.1.0 or something like that.

The only issue I see here is that router A (which is interconnected with B, although I dont know if I should interconnect them) learns the 192.168.1.0 route through B and would send packets to B to reach this network, but this is just a matter of administrative distance.

Can you tell me what kind of erroneous info the A and B redistributes into RIPv2 domain to make it a route feedback loop and how to see the effect of this routing information?

[Muhammad Thanveer]

Dear Friend when your ripv2 routes are redistributed into ospf at router A the routes has become OE2 and now as you also have redistributed them as same at Router B.

Router A and B is learning the routes of ripv2 via protocol ripv2 and again the two routers are learning them via opf protocol also.

and rip bieng 120 and ospf being 110 the routes learned in to ospf are taken preference.

for that reason as router and b has protocol ospf running in between router a is learning the route via router b.

Here we should avoid the loop, you can do this by redistributing only at router A or router B not at the both routers.

other wise create an access list and deny subnetw 10.10.10.0/24,10.10.12.0/24,10.10.10.15.0/24 and call it in route map and place it at router Bs rip, it means router Bs rip will not learn that subnets from rip but it learns from ospf.

and do it vice versa at router A for the subnets listed below in the diagram.

in the diagram you have same subnets 10.10.13.0/24 at two places  if you are configuring in the same manner there is a posibility of loop if you are not using vrfs. if it just a mistake innthe diagram that is ok and i have consifered the above 10.10.13.0/24 as 10.10.15.0/24 and answered this.

Hope you understand

Please rate the posts

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

[Vadym Belyayev]

Muhammad, thank you very much for your reply.

Can you tell me, why is this called a loop, since we only have 1 route in the OSPF table? The traffic is making it toward the destination always, without any problem.

It is true that if a router runs both protocols, it will learn the same routes via OSPF with lower AD, so from the point of view of system resources, it is probably more convinient for the router not to learn the same info via 2 routing protocols.

But I do not see a loop here. Maybe it is not a loop, but a term for Route Feedback concept.

[Muhammad Thanveer]

Hmm, You are correct dear.

But by the help of route-map we can atleast tweak the protocol not to learn the routes by this we may avoid the route feedback loop, this is what I thought.

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

[Vadym Belyayev]

Thank you Muhammad,

I found something very simple to understand about this topic. I should have searched better

https://learningnetwork.cisco.com/thread/8836

[Muhammad Thanveer]

You made a query here that helped me too.....

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."